Electrical currents having high amperage and in the form of one or more pulses of relatively short duration are useful for many applications. Typical applications include, but are not limited to, use as a power supply for a rail gun, to launch payloads into space, or to accelerate components to very high velocities (e.g. Mach 10) for structural testing. Heretofore, a typical power supply system for producing high amperage pulses has included a rotor/stator system having electromagnets that are mounted on the rotor, and electric windings that are mounted on the stator. For these systems, an external motor is generally used to turn the rotor about a rotation axis. During most of this rotation, the electric windings are switched into an open circuit state so that no current flows through the electric winding. When a current pulse is required, however, the electromagnets on the rotor are energized. Thereafter, the electric winding is quickly connected to a load (e.g. rail gun) to close a circuit that includes both the winding and the load. For some applications, the rotor must be held at a relatively high rotational velocity for a long period of time until a current pulse is needed.
In greater detail, generation of an electrical current occurs due to the interaction between the electric windings on the stator and a time-varying magnetic field that is generated by the rotating electromagnets. Typically, when the electric winding is connected to the load, a high amperage current pulse of relatively short duration is passed through the load. This pulse power extraction drastically reduces the rotational speed of the rotor, which results in a falling exit voltage.
A common design that has been previously utilized for high amperage pulse production has included a geometry that was borrowed from state of the art electric alternators and motor designs. In this geometry, a drum-shaped rotor having a relatively long axial length and relatively short diameter is used. Also, for this design, the electromagnets are positioned at or near the circumference of the rotor and the stator is formed with a surface that is shaped and positioned to surround the cylindrical surface of the drum. With this structure, the magnetic field generated by the electromagnets radially crosses a circumferential gap between the rotor and the stator to intersect the stator windings.
At this point, for the structure described above, it is worthwhile to note that both the magnitude of the generated current as well as the length of the pulse duration will depend on many factors including the size of the field generated by the electromagnets, and the diameter, weight and rotational speed of the rotor. Indeed, heretofore, to generate a high amperage current, relatively heavy, high-speed rotors have been used that are generally supported by at least two heavily loaded, high-speed bearings. These high-speed bearings typically require constant cooling which can be expensive and often require significant maintenance.
Another disadvantage presented by the above-described structure arises due to the fact that a relatively large current must be used to energize the electromagnets that rotate with the rotor. Specifically, these currents typically generate substantial amounts of ohmic heat that must be dissipated and removed from the rotor. Additionally, in order to supply this direct current to the rotating electromagnets, slip rings and brushes have generally been required. Unfortunately, these slip rings and brushes are required to work continuously and at high speeds, even when the electromagnets are not energized. As a consequence, the brushes and slip rings tend to wear quickly and require frequent replacement.
Another drawback associated with the structure described above concerns the positioning of the electromagnets at the circumference of the rotor. With this positioning, the electromagnets are exposed to large centrifugal forces during the high speed rotation of the rotor. Indeed, in some cases, these centrifugal forces can be so strong as to require the use of retaining bands to hold the electromagnets in place. Unfortunately, these retaining bands often intrude into the gap between the electromagnets and the current windings, requiring the use of a gap that is wider than the optimum theoretical gap width. The result of this non-optimal gap width is that the induced voltage in the current windings is significantly less than what it could otherwise be with an optimal gap width. (i.e. without retaining bands).
Another factor that must be considered when contemplating the design of a device having a large rotating mass is the substantial reaction moments that are created when the rotor rapidly decelerates. These reaction moments are transferred to the platform that the device is mounted on. For the case where the platform is a vehicle (e.g. tank, small ship, etc) these reaction moments can be disruptive. To obviate this concern, two identical, counter-rotating devices can be mounted on a single platform to allow the rotating masses to be simultaneously decelerated to produce offsetting reaction moments. Lastly, for vehicle-mounted systems having heavy rotors which rotate about a horizontal rotation axis, these rotors act as gyroscopes and can disrupt vehicle steering. This can be overcome by designing a device in which the rotor(s) rotate about a substantially vertical axis.
In light of the above, it is the object of the present invention to provide an energy storage and pulse power supply system that does not require rotating windings and, thus, does not require a sub-system to dissipate and remove ohmic heat from a rotating machine part, or the use of high-speed, high-current slip rings and brushes. It is another object of this invention to provide an energy storage and pulse power supply system having an optimal gap width between the magnets and the current windings. Yet another object of the present invention is to provide systems and methods for generating, storing and converting stored kinetic energy into electrical energy which are easy to use, relatively simple to implement, and comparatively cost effective.